To prevent dust particles from affecting product quality, many electronic products are generally placed in a dust-free room to filtrate solid particle impurities such as dust in air. As shown in FIG. 1, the dust-free room is configured with fan filter units (FFUs) at a top of a factory, namely a fan is combined with a filter (high efficiency particulate air filter (HEPA)) or an ultra low penetration air filter (ULPA)) to form an end purification equipment that uses self-supplied power. Air is sucked in by the fan from the FFU top and is filtrated by the HEPA, and the filtrated air is uniformly delivered at an air speed of 0.45 m/s±20% from an air outlet surface. When the FFUs filtrate particulates in the air, large dust particulates are blocked inside the and clean air is outputted. Most of the FFUs are scrapped because of built-up of the dust particles, which requires the FFUs to be serviced frequently.